1. Field of the Invention
The present invention relates to a fuel evaporator for a fuel cell system. More particularly, the present invention relates to a fuel evaporator to heat and evaporate a raw liquid fuel.
2. Prior Art
In recent years, it has come to our notice that a fuel cell system FCS is a power generator that causes less contamination in global environment. The fuel cell system is a system to take out an electric energy produced by a chemical reaction from a fuel gas with oxygen. The fuel gas such as hydrogen is supplied to a fuel cell together with an oxidized gas containing oxygen to produce an electric energy.
However, as well known, it is not easy to store or treat hydrogen gas or liquefied hydrogen gas. For this reason, a modified gas is used as a fuel. The modified gas is prepared by evaporating a raw liquid fuel (hereinafter referred to only as liquid fuel) such as methanol by means of an evaporator.
The applicant of the present invention has disclosed a fuel evaporator to prepare a fuel gas by evaporating a liquid fuel in the unexamined patent application Hei 11-125366 in Japan. The fuel evaporator is explained in the accompanied drawing FIG. 1.
In FIG. 1 reference numeral 100 indicates an evaporator. The evaporator comprises an evaporation chamber 111 to evaporate the liquid fuel FL (indicated with reference letter FL in FIG. 1) by the heat of combustion gas HG (indicated with reference letter HG in FIG. 1) generated by a combustion apparatus (not shown) and a superheating chamber 130 which is located next to the evaporation chamber 111 to superheat the fuel gas FG (indicated with reference letter FG in FIG. 1) evaporated in said evaporation chamber 111. A combustion gas HG passage 113 is provided along the under surface of a bottom 111b of said evaporation chamber 111. The combustion gas passage 113 is communicated with said evaporation chamber 111 and said superheating chamber 130 to lead the gas passing said evaporation chamber 111 into said superheating chamber 130. The combustion gas HG fed into said superheating chamber 130 is applied to superheat the fuel gas FG in said superheating chamber 130.
There are provided in said evaporation chamber 111 a plurality of heating medium tubes 112, 112 . . . to supply highly heated combustion gas HG issued from the combustion apparatus (not shown) and a fuel injector 140 which injects the liquid fuel FL diffusively to a plurality of heating medium tubes 112, 112 . . .
Each of said heating medium tubes 112, 112 . . . substantially has a configuration of U tube. Each of Said heating medium tubes is arranged in lattice form with each other in upper and lower direction as well as in width direction in said evaporation chamber 111. An inlet 112A and an outlet 112B of the combustion gas HG of said heating medium tubes are provided on a wall surface 110B of said evaporation chamber 111.
There are provided a plurality of steam tubes 131, 131 . . . in the superheating chamber 130 to lead the fuel gas FG generated in said evaporation chamber 111.
The heated combustion gas FG introduced to the lower part of said superheating chamber 130 through a passage 113 is exhausted from the outlet located in the upper part of said superheating chamber 130. The combustion gas HG is heated by contact with the surface of the steam tubes 131,131.
In the case of evaporation of the liquid fuel FL by means of the evaporator 100, said liquid fuel FL is injected from a fuel injector 140 to the heating medium tubes 112, 112 . . . Said liquid fuel FL injected from the fuel injector 140 is evaporated by contacting said heating medium tubes 112, 112 . . . and a bottom surface 111b and is introduced into the superheating chamber 130. The fuel gas FG is led into a modifier (not shown) after being superheated by the combustion gas HG in the superheating chamber 130. (Direction of fuel gas FG is indicated by reference arrow in the right side of FIG. 1.)
However, it has been pointed that to diffuse the liquid fuel FL equally in said evaporation chamber 111 is difficult because said heating medium tubes 112, 112 . . . are located separately from the injection holes of the fuel injector 140. Also, it is difficult to inject the liquid fuel FL effectively to an area where the heat is concentrated in said evaporation chamber 111. Thus, an evaporation efficiency of the liquid fuel FL is decreased and total efficiency of the system is accordingly decreased. Further, it has been pointed as a defect that an output shortage is generated when load of the fuel cell system is increased.
Further, a liquid reservoir is sometimes generated when the liquid fuel is injected apart from a heat concentrated part in the evaporation chamber 111 and the liquid fuel is retained on the wall or the bottom of said evaporation chamber 111 in liquefied state. When a liquid film is created from such liquefied state, the liquid film decreases the heat receiving area in comparison with liquid dropping condition and it becomes difficult to evaporate the liquid fuel. In these cases, an excess fuel gas gradually evaporated from the liquid reservoir is naturally supplied to the fuel cell system, and even if amount of the liquid fuel to be supplied is decreased as the load of the fuel cell system is decreased, it becomes difficult to control the amount of the fuel gas to be exactly supplied. Accordingly, the responsibility of the fuel cell system to output variation becomes worse.
Further, because of construction provided with the superheating chamber in the latter step of the evaporation chamber the passages of the combustion gas becomes complicated. Such complicated combustion gas passages decrease heat efficiency of the combustion gas as the heat is deprived outside the apparatus. It goes without saying that the heat efficiency of the combustion gas becomes poor.
The present invention has been made with the foregoing background in mind. The object of the present invention is to offer a fuel evaporator to evaporate the liquid fuel efficiently and rapidly by improving an injection property of the liquid fuel in the evaporator.
It is also an object of the present invention to offer an excellent evaporator in heating efficiency of the combustion gas in a simple construction.
The present invention, in order to solve the aforementioned problem, comprises an evaporation chamber to prepare a fuel gas by evaporating said liquid fuel with a heating medium of high temperature, a fuel injector to supply said liquid fuel to an evaporation chamber, said liquid fuel being passed through the evaporation chamber, a plurality of heating medium tubes through which the heat medium of high temperature is passed, and an exhaust port, through which the fuel gas being exhausted. The fuel injector is provided at the side of the evaporation chamber. The fuel injector is also provided with fuel injection tubes extending into the evaporation chamber and the fuel injection tubes are provided with a plurality of injection holes.
According to the aforementioned composition it has become possible to inject the liquid fuel equally into the evaporation chamber through the plurality of the injection holes provided on the fuel injection tubes extended into the evaporation chamber. It has become possible to evaporate the liquid fuel efficiently and rapidly.
The fuel injection tubes are arranged to cross at right angle with respect to the heating medium tubes. With this arrangement the liquid gas is diffused equally to the areas of substantially same temperature. Thus heat efficiency is improved and the liquid fuel is rapidly evaporated.
Particularly, in the case of the heat medium tubes having a bellows shape are applied, the liquid fuel contacts vertical surfaces of the bellows and the liquid fuel is effectively evaporated.
In the above composition it is preferred to provide injectors having larger diameter and numerous holes in the vicinity of central part of the fuel injection tubes than the side part near the wall of the evaporation chamber.
With such composition of fuel injection tubes much amounts of the liquid fuel are injected to the central area of the evaporation chamber where the heat is concentrated.
Further, with the aforementioned composition, it is preferable to have a superheat part in the evaporation chamber and yet the heating medium tubes are applied in such a superheat part.
With the aforementioned composition the present invention has offered a highly heat efficient evaporator so as to evaporate the liquid fuel effectively and rapidly.
Further, in such an aforementioned composition it is recommended to apply a catalyst combustion apparatus. If the catalyst combustion apparatus is provided at lower part of the evaporation chamber, the heat to be diffused in the circumstance is effected as a heating source of evaporation chamber. Thus heating efficiency is improved and the liquid fuel is evaporated efficiently and rapidly.